Does ammonium nitrogen affect accumulation, subcellular distribution and chemical forms of cadmium in Kandelia obovata?

Application of rhizobium inoculation in regulating heavy metals in legumes: A meta-analysis

Rhizobium inoculation has been widely applied to alleviate heavy metal (HM) stress in legumes grown in contaminated soils, but it has generated inconsistent results with regard to HM accumulation in plant tissues. Here, we conducted a meta-analysis to assess the performance of Rhizobium inoculation for regulating HM in legumes and reveal the general influencing factors and processes. The meta-analysis showed that Rhizobium inoculation in legumes primarily increased the total HM uptake by stimulating plant biomass growth rather than HM phytoavailability. Inoculation had no significant effect on the average shoot HM concentration (p > 0.05); however, it significantly increased root HM uptake by 61 % and root HM concentration by 7 % (p < 0.05), indicating safe agricultural production while facilitating HM phytostabilisation. Inoculation decreased shoot HM concentrations and increased root HM uptake in Vicia, Medicago and Glycine, whereas it increased shoot HM concentrations in Sulla, Cicer and Vigna. The effects of inoculation on shoot biomass were suppressed by nitrogen fertiliser and native microorganisms, and the effect on shoot HM concentration was enhanced by high soil pH, organic matter content, and phosphorous content. Inoculation-boosted shoot nutrient concentration was positively correlated with increased shoot biomass, whereas the changes in pH and organic matter content were insufficient to significantly affect accumulation outcomes. Nitrogen content changes in the soil were positively correlated with changes in root HM concentration and uptake, whereas nitrogen translocation changes in the tissues were positively correlated with changes in HM translocation. Phosphorus solubilisation could improve HM phytoavailability at the expense of slight biomass promotion. These results suggest that the diverse growth-promoting characteristics of Rhizobia influence the trade-off between biomass-HM phytoavailability and HM translocation, impacting HM accumulation outcomes. Our findings can assist in optimising the utilisation of legume-Rhizobium systems in HM-contaminated soils.

Phytoremediation Potential of Flax Grown on Multimetal Contaminated Soils: A Field Experiment

The aim of this study was to assess the phytoremediation potential of fiber flax (Linum usitatissimatum L., var. Calista) cultivated in a soil contaminated with multiple metals, under real field conditions. A two-year (2022 and 2023) field experiment was conducted in a site contaminated with elevated concentrations of Cd, Ni, Cu, Pb, and Zn due to mining and metallurgical activities. Three different nitrogen fertilization levels were tested (N0: 0 kg N ha-1, N1: 30 kg N ha-1, N2: 60 kg N ha-1), and both spring and winter sowings were conducted. At full maturity, growth parameters and yields were measured. The phytoremediation potential of flax was assessed in terms of the metal concentrations in the above-ground biomass and of the metal uptake (i.e., the potential removal of the soil metals in g ha-1 and per year). Flax demonstrated a shorter growth cycle, with shorter and thicker plants and higher yields when sown in spring compared to winter sowing. Plant growth and productivity were not evidently influenced by additional nitrogen fertilization during plant growth. The cadmium bioaccumulation factor was 1.06, indicating that flax accumulates this metal. For Ni, Cu, Pb, and Zn, the corresponding values were 0.0, 0.04, 0.004, and 0.02, suggesting that this crop excludes these metals. The order of the higher uptake in plant tissues was as follows: Zn > Pb > Cd > Cu > Ni. In conclusion, flax demonstrated tolerance to heavy metals in the soil, effectively supporting soil restoration through cultivation. Additionally, flax showed potential as a cadmium accumulator while excluding nickel, copper, lead, and zinc.

Enhancing soil health to minimize cadmium accumulation in agro-products: the role of microorganisms, organic matter, and nutrients

Agro-products accumulate Cd from the soil and are the main source of Cd in humans. Their use must therefore be minimized using effective strategies. Large soil beds containing low-to-moderate Cd-contamination are used to produce agro-products in many developing countries to keep up with the demand of their large populations. Improving the health of Cd-contaminated soils could be a cost-effective method for minimizing Cd accumulation in crops. In this review, the latest knowledge on the physiological and molecular mechanisms of Cd uptake and translocation in crops is presented, providing a basis for developing advanced technologies for producing Cd-safe agro-products. Inoculation of plant growth-promoting rhizobacteria and arbuscular mycorrhizal fungi, application of organic matter, essential nutrients, beneficial elements, regulation of soil pH, and water management are efficient techniques used to decrease soil Cd bioavailability and inhibiting the uptake and accumulation of Cd in crops. In combination, these strategies for improving soil health are environmentally friendly and practical for reducing Cd accumulation in crops grown in lightly to moderately Cd-contaminated soil.

Multimedia distribution, partitioning, sources, comprehensive toxicity risk and co-occurrence network characteristics of trace elements in a typical Chinese shallow lake with high antibiotic risk

Although the combined pollution of trace elements and antibiotics has received extensive attention, the fate and toxicity risk of trace elements with high antibiotic risk are still unclear. The multimedia distributions, partitioning, sources, toxicity risks and co-occurrence network characteristics of trace elements in surface water (SW), overlying water (OW), pore water (PW) and sediment (Sedi) samples of 61 sites from Baiyangdian (BYD) Lake were investigated. The trace elements in the SW and OW are derived mainly from traffic and agricultural sources, and those in PW and Sedi samples are primarily from lithogenic and industrial sources. The total toxicity risk index (TRI) of nine trace elements (ΣTRI) in Sedi samples showed a very high toxicity risk (18.35 ± 8.84), and a high combined pollution toxicity risk (ΣΣTRI) was observed in PW (149.17 ± 97.52) and Sedi samples (46.37 ± 24.00). The co-occurrence network from SW to PW became more vulnerable. Generally, total antibiotics and TP may be keystones of trace elements in water and sediment. The high antibiotic risk significantly influenced ΣΣTRI in water samples but not in Sedi samples. The findings provide new implications for the monitoring and control of combined antibiotic-trace element pollution in shallow lakes.

Mathematical Estimation of Endogenous Proline as a Bioindicator to Regulate the Stress of Trivalent Chromium on Rice Plants Grown in Different Nitrogenous Conditions

The accumulation of proline impacts the defense mechanisms of plants against the harmful effects of adverse environmental conditions; however, its concentration in plants is associated with the metabolism of N. Therefore, the effects of exogenous organic [glutamate (Glu)/arginine (Arg)] and inorganic [nitrate (NO3-)/ammonium (NH4+)] N on the accumulation of proline (Pro) in rice plants under trivalent chromium [Cr(III)] stress were studied through using the mass balance matrix model (MBMM). Application of 'NH4+' showed the largest contribution to the Pro content in rice shoots under different concentrations of Cr(III), followed by 'NO3-', 'Arg', and 'Glu' applications. On the other hand, 'Arg' application displayed the largest contribution to the Pro content in roots under Cr(III) stress, followed by 'NH4+', 'Glu', and 'NO3-' applications. The combined application of 'NH4++Arg' showed the greatest contribution to the Pro content in both roots and shoots of Cr(III)-treated rice seedlings, while the application of 'NO3-+Glu' showed the least contribution to the Pro content in rice seedlings. The current study indicated that the endogenous level of Pro in rice seedlings is quite sensitive to Cr(III) stress under different N sources, and the mathematical modeling showed a reliable result while estimating the relationship between Pro content and N source application.

Migration and transformation of Cd in four crop rotation systems and their potential for remediation of Cd-contaminated farmland in southern China

A crop rotation system combining agricultural production with phytoremediation is an economical and sustainable method of remediation of cadmium (Cd)-contaminated farmland. This study focuses on migration and transformation of Cd in rotation systems and the influencing factors. In a two-year field experiment, four rotation systems were evaluated: traditional rice and oilseed rape (TRO), low-Cd rice and oilseed rape (LRO), maize and oilseed rape (MO), and soybean and oilseed rape (SO). Oilseed rape is a remediation plant in rotation systems. Compared to 2020, the grain Cd concentrations of traditional rice, low-Cd rice, and maize in 2021 decreased by 73.8 %, 65.7 %, and 24.0 % (below the safety limits), respectively. However, soybean increased by 71.4 %. The LRO system featured the highest oil content of rapeseed (about 50 %) and economic output/input ratio (1.34). Removal efficiency of total Cd in soil was 10.03 % (TRO) > 8.3 % (LRO) > 5.32 % (SO) > 3.21 % (MO). Crop uptake of Cd was influenced by bioavailability of soil Cd, and soil environmental factors regulated the bioavailable Cd. Redundancy analysis (RDA) indicated that soil nitrate‑nitrogen (NO₃^--N) had a dominant impact on bioavailable Cd in soil, with variance contributions of 56.7 % for paddy-upland (TRO and LRO) and 53.5 % for dryland (MO and SO) rotation systems. The difference reflected that ammonium N (NH₄⁺-N) was a secondary factor in paddy-upland rotations, while it was the available phosphorus (P) in dryland rotations, with variance contributions of 10.4 % and 24.3 %, respectively. The comprehensive evaluation of crop safety, production, economic benefits, and remediation efficiency revealed that the LRO system was efficient and more acceptable to local farmers, providing a new direction for the utilization and remediation of Cd-contaminated farmland.

The role of nickel in cadmium accumulation in rice

Rice is one of the world's staple foods. Cadmium (Cd) levels in paddy soil are still increasing, and "Cd-contaminated rice" is a frequent occurrence, posing a serious threat to human health. Therefore, Cd contamination in rice is a key issue in agricultural production that needs to be addressed urgently. The Cd accumulation in rice is closely related to other elements. In this study, the impact of nickel (Ni) on the uptake and accumulation of Cd in rice was revealed, and the mechanism was discussed. Statistical analysis of field data showed that Cd concentration in rice grains decreased exponentially with increasing Ni concentration in paddy soils, which was verified by the hydroponic experiments. Under 5 μmol/L Cd exposure conditions, the addition of Ni (100 μmol/L) reduced the Cd contents in roots, stems, and leaves by 81.6 %, 60.6 %, and 65.9 %, respectively. With the presence of Ni, the amount of iron plaque decreased, and the Cd content in the iron plaque was reduced due to the competition between Ni and Cd for adsorption sites. In addition, the migration of Cd from stems to leaves was reduced. At the same time, the distribution of Cd in the cell was altered, and the concentration of Cd in the root cell walls increased with increasing Ni addition under 5 μmol/L Cd exposure. These findings highlight the critical role of Ni in inhibiting Cd accumulation in rice, and provide important information for understanding the effects of coexisting elements in Cd-contaminated soils on Cd accumulation in crops.

Nitrogen and sulfur fertilizers promote the absorption of lead and cadmium with Salix integra Thunb. by increasing the bioavailability of heavy metals and regulating rhizosphere microbes

Fertilization is an effective agronomic strategy to improve the efficiency of phytoextraction by Salix integra Thunb. However, the specific effects of the simultaneous application of nitrogen (N) and sulfur (S) fertilizers in the rhizosphere remain unclear. We investigated the bioavailability of lead (Pb) and Cadmium (Cd) along with the microbial metabolic functions and community structure in the rhizosphere soil of S. integra after the application of N (0, 100, and 200 kg·ha⁻¹·year⁻¹) and S (0, 100, and 200 kg·ha⁻¹·year⁻¹) fertilizers for 180 days. The simultaneous application of N and S fertilizers significantly enhanced the absorption of Pb and Cd by S. integra, whereas this effect was not observed for the single application of N or S fertilizer. The contents of acid-soluble Pb and Cd in the rhizosphere soil significantly increased after either single or combined fertilize applications. The microbial metabolic activity was enhanced by the N and S fertilizers, whereas the microbial diversity markedly decreased. The metabolic patterns were mainly affected by the concentration of N fertilizer. The dominant fungi and bacteria were similar under each treatment, although the relative abundances of the dominant and special species differed. Compared to the N200S100 and N200S200 treatments, the N100S100 and N100S200 treatments resulted in fewer pathogenic fungi and more rhizosphere growth-promoting bacteria, which promoted phytoremediation by S. integra. Redundancy analysis indicated that the pH and nitrate content were the key factors affecting the structure of the microbial community. Collectively, the results suggest interactive effects between N and S fertilizers on the rhizosphere soil, providing a potential strategy for plant-microbial remediation by S. integra.

Ammonium has stronger Cd detoxification ability than nitrate by reducing Cd influx and increasing Cd fixation in Solanum nigrum L

Cadmium (Cd) is a harmful heavy metal that affects the growth and development of plants. Nitrogen (N) is an essential nutrient for plants, and appropriate N management can improve Cd tolerance. The aim of our study was to explore the effects of different forms of N on the molecular and physiological responses of the hyperaccumulator Solanum nigrum to Cd toxicity. Measurement of biomass, photosynthetic parameters, and Cd²⁺ fluxes using non-invasive micro-test technique, Cd fluorescent dying, biochemical methods and quantitative real-time PCR analysis were performed in our study. Our results showed that ammonium (NH₄⁺) has stronger Cd detoxification ability than nitrate (NO₃^-), which are likely attributed to the following three reasons: (1) NH₄⁺ decreased the influx and accumulation of Cd²⁺ by regulating the transcription of Cd transport-related genes; (2) the ameliorative effects of NH₄⁺ were accompanied by the increased retention of Cd in the cell walls of roots; and (3) NH₄⁺ up-regulated SnExp expression.

Nitrogen addition alleviated sexual differences in responses to cadmium toxicity by regulating the antioxidant system and root characteristics, and inhibiting Cd translocation in mulberry seedlings

Cadmium (Cd) toxicity and nitrogen (N) deposition are two major environmental stresses which can affect plant growth. It's less clear that how the combined Cd accumulation and N deposition affect the male and female plants of dioecious species. The aim of the present study was to detect sex-specific responses to Cd stress and simulated N deposition in one-year-old male, female and hermaphrodite seedlings of Morus alba. Changes in morphology, physiology, root architecture and biomass of the three sex types of mulberry seedlings were determined. The results showed that Cd toxicity caused limited growth, impaired photosynthetic apparatus and decreased gas exchange rates with significant sex-specific differences. Mulberry was found to deploy detoxification mechanisms to avoid or tolerate toxic Cd effects through the activation of the antioxidant system, increasing proline and non-protein thiol contents, translocating Cd into different plant parts and decreasing biomass. Females displayed a low tolerance to high Cd and were more sensitive to Cd stress. Simulated N deposition alleviated the negative effects of Cd on leaves and decreased sex-specific differences in the three kinds of mulberry seedlings, but N fertilizer did not affect the total biomass. The N-stimulated increasing in proline and non-protein thiol contents might play a crucial role in resisting the damage caused by Cd stress, and the three kinds of mulberry seedlings had slightly different ways of improving Cd tolerance by N deposition. Sexual differences in Cd accumulation are correlated with root architecture. This study provides evidence for the utilization of mulberry to treat Cd-contaminated soils under N deposition.

Nitrogen in plants: from nutrition to the modulation of abiotic stress adaptation

Nitrogen is one of the most important nutrient for plant growth and development; it is strongly associated with a variety of abiotic stress responses. As sessile organisms, plants have evolved to develop efficient strategies to manage N to support growth when exposed to a diverse range of stressors. This review summarizes the recent progress in the field of plant nitrate (NO3-) and ammonium (NH4+) uptake, which are the two major forms of N that are absorbed by plants. We explore the intricate relationship between NO3-/NH4+ and abiotic stress responses in plants, focusing on stresses from nutrient deficiencies, unfavorable pH, ions, and drought. Although many molecular details remain unclear, research has revealed a number of core signaling regulators that are associated with N-mediated abiotic stress responses. An in-depth understanding and exploration of the molecular processes that underpin the interactions between N and abiotic stresses is useful in the design of effective strategies to improve crop growth, development, and productivity.

Ammonium-nitrogen addition at the seedling stage does not reduce grain cadmium concentration in two common wheat (Triticum aestivum L.) cultivars

High cadmium (Cd) concentration in common wheat (Triticum aestivum L.) grains poses potential health risks. Several management strategies have been used to reduce grain Cd concentration. However, limited information is available on the use of ammonium-nitrogen (NH₄⁺-N) as a strategy to manage Cd concentration in wheat grains. In this study, NH₄⁺-N addition at the seedling stage unchanged the grain Cd concentration in the high-Cd accumulator, Zhoumai 18 (ZM18), but dramatically increased that in the low-Cd accumulator, Yunmai 51 (YM51). Further analysis revealed that the effects of NH₄⁺-N addition on whole-plant Cd absorption, root-to-shoot Cd translocation, and shoot-to-grain Cd remobilization were different between the two wheat cultivars. In ZM18, NH₄⁺-N addition did not change whole-plant Cd absorption, but inhibited root-to-shoot Cd translocation and Cd remobilization from lower internodes, lower leaves, node 1, and internode 1 to grains via the down-regulation of yellow stripe-like transporters (YSL), zinc transporters (ZIP5, ZIP7, and ZIP10), and heavy-metal transporting ATPases (HMA2). This inhibition decreased the grain Cd content by 29.62%, which was consistent with the decrease of the grain dry weight by 23.26%, leading to unchanged grain Cd concentration in ZM18. However, in YM51, NH₄⁺-N addition promoted continuous Cd absorption during grain filling, root-to-shoot Cd translocation and whole-plant Cd absorption. The absorbed Cd was directly transported to internode 1 via the xylem and then re-transported to grains via the phloem by up-regulated YSL, ZIP5, and copper transporters (COPT4). This promotion increased the grain Cd content by 245.35%, which was higher than the increased grain dry weight by 132.89%, leading to increased grain Cd concentration in YM51. Our findings concluded that the addition of NH₄⁺-N fertilizer at the seedling stage is not suitable for reducing grain Cd concentration in common wheat cultivars.

The combined use of arbuscular mycorrhizal fungi, biochar and nitrogen fertilizer is most beneficial to cultivate Cichorium intybus L. in Cd-contaminated soil

We assessed Cichorium intybus L. (chicory) growth, nutrients and Cd uptake in the presence of arbuscular mycorrhizal fungi (AMF), biochar (BC) and nitrogen (N) fertilizer applications in experimental pot studies. Mycorrhizal colonization was improved by BC addition but not N addition. However, in the presence of AMF, BC and N had positive effects on shoot biomass and plants grown in the presence of all 3 components yielded the highest levels of shoot biomass compared to pair-wise combinations or individual components singly added. AMF inoculation also increased root biomass and this effect was apparent in the combinations that included AMF without BC. Fungal inoculation also led to increased contents of phosphorus (P), magnesium (Mg) and copper (Cu) in both chicory shoots and roots and potassium (K) and manganese (Mn) in roots. Moreover, in the presence of BC, AMF inoculation evidently enhanced the shoot Ca content. In contrast, the presence of AMF inhibited plant Cd absorption and BC addition further inhibited root Cd concentration following the AMF inoculation. Applying N fertilizer alone increased Cd transfering from soil to plants. However, when combined with use of AMF and BC, Cd toxicity to plants was reduced. This study demonstrated that AMF inoculation combined with BC and N fertilizer could improve chicory growth, nutrient absorption and reduction of Cd uptake in Cd-contaminated soil.

Enhancement of cadmium accumulation in sweet sorghum as affected by nitrate

The Cadmium (Cd)-polluted soils are is an increasing concern worldwide. Phytoextraction of Cd pollutants by high biomass plants, such as sweet sorghum, is considered an environmentally-friendly, cost-effective and sustainable strategy for remediating this problem. Nitrogen (N) is a macronutrient essential for plant growth, development and stress resistance. Nevertheless, how nitrate, as an important form of N, affects Cd uptake, translocation and accumulation in sweet sorghum is still unclear. In the present study, a series of nitrate levels (N1, 0.5 mm; N2, 2 mm; N3, 4 mm; N4, 8 mm and N5, 16 mm) with or without added 5 μm CdCl₂ treatment in sweet sorghum was investigated hydroponically. The results indicate that Cd accumulation in the aboveground parts of sweet sorghum was enhanced by optimum nitrate supply, resulting from both increased dry weight and Cd concentration. Although root-to-shoot Cd translocation was not enhanced by increased nitrate, some Cd was transferred from cell walls to vacuoles in leaves. Intriguingly, expression levels of Cd uptake and transport genes, SbNramp1, SbNramp5 and SbHMA3, were not closely related to increased Cd as affected by nitrate supply. The expression of SbNRT1.1B in relation to nitrate transport showed an inverted 'U' shape with increasing nitrate levels under Cd stress, which was in agreement with trends in Cd concentration changes in aboveground tissues. Based on the aforementioned results, nitrate might regulate Cd uptake and accumulation through expression of SbNRT1.1B rather than SbNramp1, SbNramp5 or SbHMA3, the well-documented genes related to Cd uptake and transport in sweet sorghum.

Different nitrogen forms differentially affect Cd uptake and accumulation in dwarf Polish wheat (Triticum polonicum L.) seedlings

This study investigated the effects of different nitrogen (N) forms on Cadmium (Cd) uptake and accumulation in dwarf Polish wheat (DPW) seedlings, which were grown under Cd stress with N-Null, NH₄⁺-N, NO₃^--N and NH₄⁺-N + NO₃^--N. We measured plant growth and determined Cd uptake, translocation, accumulation, subcellular distribution and chemical forms in the roots and shoots of DPW seedlings. We also analyzed saccharide concentrations, and the transcript levels of genes encoding metal transporters in the roots of DPW seedlings. In the absence of NO₃^--N, addition of NH₄⁺-N reduced roots Cd concentration, F_CW (Cd in cell wall), F_S (Cd in soluble fraction) and F_E (inorganic Cd) concentrations, and induced the expression of four genes encoding metal transporters in roots, while it promoted Cd translocation to shoots. In the presence of NO₃^--N, addition of NH₄⁺-N increased roots Cd concentration, F_CW and F_W concentrations, and induced the expression of 22 genes encoding metal transporters in roots. Regardless of NH₄⁺-N level, addition of NO₃^--N increased roots Cd concentration, F_CW, F_S, F_W (water-soluble Cd), F_NaCl (pectates and protein Cd), F_HAc (undissolved Cd phosphate) and lactose concentrations, and also induced the expression of genes encoding metal transporters in roots. Overall, NH₄⁺-N differently regulated Cd uptake and accumulation in DPW seedlings in the absence or presence of NO₃^--N, while NO₃^--N greatly increased Cd uptake and accumulation in the presence of NH₄⁺-N compared to the absence of NH₄⁺-N. These patterns of Cd alteration likely arose due to different N forms altering Cd subcellular distribution and chemical forms, lactose concentration and the expression of metal transporter genes.

Reducing Cd accumulation in rice grain with foliar application of glycerol and its mechanisms of Cd transport inhibition

Excessive cadmium (Cd) in rice grain has become a major global public health problem. Here, the effect of foliar glycerol application on Cd accumulation in brown rice was examined. Various spraying concentrations of glycerol between 0.4mM and 50mM were investigated and the results showed that 0.8 mM was the best application concentration for decreasing Cd content in brown rice. After different application period experiment, filling stage was considered as the optimal spraying time. 0.4mM-5mM glycerol application one time at the filling stage could significantly reduce Cd concentration in brown rice by 28.5%-60.4%. Cd transport factors (the ratio of brown rice and flag leaf/node) were decreased by 48.5% and 27.3%, respectively, with glycerol application. Glycerol application also significantly increased Cd concentration in soluble fraction in flag leaf while reduced inorganic Cd and water-soluble Cd in both flag leaf and stem. Our results showed foliar spraying glycerol inhibited Cd transport to brown rice through Cd compartmentalisation in the vacuole and transformation of cadmium chemical form. This study may provide a new method to effectively alleviate the problem of excessive Cd in rice.

Responses of glutathione and phytochelatins biosysthesis in a cadmium accumulator of Perilla frutescens (L.) Britt. under cadmium contaminated conditions

Screening new accumulators of heavy metal and identifying their tolerance, enrichment capacity of heavy metals are currently hot issues in phytoremediation research. A series of hydroponic experiments were conducted to analyze the effects of glutathione and phytochelatins in roots, stems, and leaves of Perilla frutescens under cadmium stress. The results showed that the non-protein thiols in roots and stems mainly existed in the form of GSH, PC₂, PC₃, and PC₄ under Cd stress condition, while in leaves they existed in the form of GSH, PC₂, and PC₃. Furthermore, the contents of GSH and PCs positively correlated with Cd, but negatively correlated with root vigor and chlorophyll content under Cd stress conditions. After 21 days of treatments, the contents of Cd in different parts of the plant were 1465.2-3092.9 mg· kg^-1 in the roots, 199.6-478.4 mg·kg^-1 in the stems and 61.3-96.9 mg· kg^-1 in the leaves at 2, 5, 10 mg·L^-1 Cd levels respectively, and the amount of Cd uptakes were up to 3547.7-5701.7 μg·plant^-1. Therefore, P. frutescens performed high capacity in Cd accumulation, and PCs played a key role in Cd tolerance. The application prospect of the plant in phytoremediation Cd polluted soil was also discussed.

Regulatory mechanisms of nitrogen (N) on cadmium (Cd) uptake and accumulation in plants: A review

Cadmium (Cd) is a heavy metal that is toxic to plants and animals. Nitrogen (N), the most significant macro-nutrient and a common input for crop production, is often excessively applied than plants' demands by farmers to obtain more economic benefits. Understanding the regulatory mechanisms of N that control Cd uptake, translocation, and accumulation may enable the development of solutions regarding Cd pollution in the trophic chain, a major and global threat to agricultural sustainability and human health. In this review, we clarified that an increased amount of N, regardless of its form, enhances Cd uptake, translocation, and accumulation in plants, and nitrate promotes Cd uptake more than any other N form. We also described that N fertilizer alters the Cd exchange capacity and the bio-available Cd content in soil; regulates nitric oxide induced divalent cation gene expression of Nramp1, HMA2, and IRT1; and changes cell wall isolation, chelation capacity, and oxidative resistance to regulate Cd accumulation in plants. By revealing the integrated interaction effects between Cd accumulation and N fertiliser use, we propose new challenges to investigate the functions and mechanisms of N in Cd-contaminated croplands and develop suitable N-fertilisation protocols to practically reduce food health risks in agricultural food production.

Influence of nitrogen forms and application rates on the phytoextraction of copper by castor bean (Ricinus communis L.)

Fertilization is an important agricultural strategy for enhancing the efficiency of phytoremediation in copper (Cu)-contaminated soils. In this study, the effects of nitrogen (N) forms, including ammonium (NH4+-N) and nitrate (NO3--N), on the growth, translocation, and accumulation of Cu in the tissues of Ricinus communis L. were investigated in pot and hydroponic experiments. The results demonstrated that higher biomass and N contents in plants were obtained when N was supplied as NO3--N rather than NH4+-N. Application of N increased the Cu content in the roots of R. communis, with a higher content after NH4+-N (53.10-64.20 mg kg-1) than NO3--N (37.62-53.75 mg kg-1) treatment. On the contrary, the levels of Cu translocation factors were much higher in NO3--fed plants (0.34-0.45) than in NH4+-fed plants (0.28-0.38). The suggested amount of N for fertilizer application is 225 kg hm-2, which resulted in the highest Cu content in R. communis and optimal plant growth. As the main Cu-binding site, root cell walls accumulated less Cu in plants treated with NH4+-N compared with NO3--N. Additionally, NH4+-N induced a higher malondialdehyde content and more severe root damage compared with NO3--N. In the leaf, a larger number of black granules, which could be protein and starch grains involved in the detoxification of Cu in R. communis, were present after NH4+-N than NO3--N treatment. These results illustrate that N forms are especially important for Cu translocation and accumulation and that immobilization and transformation of Cu in roots were improved more by NH4+-N than NO3--N. In conclusion, N fertilizers containing the appropriate forms applied at suitable rates may enhance the biomass and Cu accumulation of R. communis and thereby the remediation efficiency of Cu-contaminated soils.

Effects of dissolved oxygen, salinity, nitrogen and phosphorus on the release of heavy metals from coastal sediments

Great amounts of nutrients discharged into the urbanized coastal areas, which are continuously subject to violently anthropogenic metal contamination, will result in eutrophication and hypoxic episode. In order to study the effects of dissolved oxygen (DO), salinity, nitrogen and phosphorus on the release of six metals including Zn, Pb, Cd, Cu, As and Cr from coastal sediments, a series of 60-days microcosm experiments consisting of sediments and seawater were conducted. Severe hypoxia could result in the enhanced peak values of Pb, Cd, Cu and Cr concentrations in the overlying water. A higher level of water salinity could elevate the peak value of As concentration in water column, and a higher level of nitrogen could increase the peak value of Zn concentration in water. The exchange fluxes demonstrated that the diffusion from the sediments was a dominant process during the first 10 days, However, a relative equilibrium of adsorption and precipitation in the sediment-water interface reached during the later periods. In addition, the bioavailability of the studied metals in sediments was elevated under severe hypoxia, or a high level of water salinity, or high levels of nitrogen and phosphorus. The results of linear regression analysis suggested that higher metal bioavailability in sediments could facilitate the metal release, but the process could be restrained by the higher aqueous phosphorus due to the precipitation of metal phosphates.

Protective effect of different forms of nitrogen application on cadmium-induced toxicity in wheat seedlings

Therefore, applying NH₄⁺-N tp PHW-SA caused greater tolerance to Cd toxicity by higher biomass production, photosynthetic capacity, Ca and Cu accumulation, better root development and lower translocation factor of Cd as well as Cd concetration in organelle fraction. The Cd stress inhibited the growth performance of wheat seedlings, the mineral nutrient accumulation, and nitrogen uptake and distribution, and different forms of nitrogen have different protective effects on wheat. In PHW-SA, ANCd treatment caused lower reduction in biomass accumulation, photosynthesis, isotope stable N content, Ca and Cu accumulation, root development inhibition, tissue Cd concentration, and transfer factor, which even led to lower concentrations of Cd in F_co than those in F_cw and F_s in comparison with NNCd treatment. On the other hand, the converse growth performance was recorded in J-11 under ANCd treatment. Meanwhile, the nitrogen absorption preference in PHW-SA was altered along with the enhanced absorption efficiency of nitrogen. Therefore, applying NH₄⁺-N to PHW-SA caused greater tolerance to Cd toxicity by higher biomass production, photosynthetic capacity, Ca and Cu accumulation, better root development and lower translocation factor of Cd as well as Cd concetration in organelle fraction..